The invention relates to an environmental control system. The invention also relates to a system for increasing the humidity of air inside an aircraft.
An environmental control system for an aircraft is designed to control airflow into the aircraft""s passenger cabin as well as air temperature inside the passenger cabin. Most aircraft environmental control systems operate on an air cycle refrigeration principle. Compressed air is obtained from a compressor stage of the aircraft""s main engine, an auxiliary power unit or some other source of air. The compressed air is cooled with ambient air to near-ambient temperature in an air-to-air heat exchanger and then expanded in an air cycle machine. Leaving the environmental control system is a stream of cooled, conditioned air, which is supplied to the passenger cabin. Although somewhat expanded, the conditioned air also pressurizes the passenger cabin.
The environmental control system also removes water vapor entrained in the air that is eventually supplied to the passenger cabin. For example, high pressure water separation can be performed on the air prior to expansion in the air cycle machine, or low pressure water separation can be performed on air leaving the air cycle machine. Removing the water vapor results in lower cabin humidity.
In certain instances, however, it might actually be desirable to increase the humidity of the air inside the passenger cabin. The air within the aircraft cabin can become dry during cruise operation. Relative humidity below 10% can occur due to low ambient humidity at altitude and excess removal of water by the environmental control system. The low humidity can cause dryness of the eyes, nose, skin and throat and other forms of discomfort for passengers and crew members inside the cabin. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) recommends a relative humidity between 30% and 60%.
However, a typical environmental control system does not increase the humidity of dry air inside the cabin.
Humidity of air inside an aircraft cabin can be increased by the present invention, which can be regarded as an integrated system including an environmental control system and a humidification system. The environmental control system includes a trim line. The humidification system includes a reverse osmosis filter, and a pump for controllably pumping water through the reverse osmosis filter. Water filtered by the reverse osmosis filter is added into the trim line of the environmental control system.